1. Field of the Invention
The present invention relates generally to a rear suspension system for motorcycles. More particularly, the invention relates to a rear suspension system for motorcycles comprising a pivotable-shaft actuated type damper and a coil spring.
2. Description of Relevant Art
A typical conventional rear suspension system for motorcycles is disposed between a relatively stationary rigid structure, for example, a vehicle body frame, and an element which is pivotably attached to the rigid structure and swingable together with vertical movement of a rear wheel, such as a rear fork. Such a system includes a shock absorber comprising an integral combination of a cylindrical damper disposed between the rear fork and an upper rear portion of the vehicle body and a coil spring fitted over the outer periphery of the damper, the shock absorber being provided so as to cushion a swinging motion of the rear fork induced by a vertical movement of the rear wheel in following undulations in the road surface, by virtue of the damping force of the cylindrical damper which is adapted to expand and contract and also by the biasing force of the coil spring.
Such a conventional shock absorber does not permit sufficient freedom of design with respect to the length of the damper, etc. For example, the amount of expansion and contraction of the cylindrical damper must be determined in accordance with the amount of pivotal movement of the rear fork. In such shock absorber, moreover, a pressure-resistant seal member is attached to a piston in the cylindrical damper to ensure a high-pressure compression by the piston of a hydraulic operating fluid, so as to generate a damping force by virtue of a throttling action of such fluid. However, a sliding resistance of such pressure-resistant seal member affects the damping characteristic of the damper when the damper expands or contracts. Further, although a coil spring is easy to manufacture and is advantageous with respect to cost, the diameter thereof is inevitably required to be large because it is fitted over the outer periphery of the cylindrical damper, thus resulting in not only an increase in the vehicle body width but also, in the event that devices such as an air cleaner, a battery and a fuel tank are disposed alongside the shock absorber, the sizes and capacities of such devices are restricted by their positional relationship to the coil spring.
The present invention effectively overcomes the foregoing problems attendant conventional rear suspension systems for motorcycles of the construction described hereinabove.